U.S. Pat. No. 5,628,169 to Stiller, assigned to The Toro Company, the assignee of this invention, discloses a pivot linkage for connecting a reel cutting unit to the frame of a reel gang mower. This pivot linkage comprises a four-bar linkage on each side of the reel cutting unit between one of the side plates of the reel cutting unit and an overlying cutting unit carrier frame. The four-bar linkages on each side of the reel cutting unit are identical to one another. Basically, the four-bar linkages serve to transmit the longitudinal propulsive force from the frame of the gang mower, namely from the cutting unit carrier frame which from a propulsion standpoint can be considered to be part of the frame of the gang mower, to the cutting unit to propel the cutting unit similarly to the gang mower, namely in a forward direction when the gang mower is moving forwardly and in a rearward direction when the gang mower is moving rearwardly. Each reel cutting unit that is attached to the frame of the reel gang mower has the same pair of four-bar linkages on opposite sides thereof.
Each four-bar linkage on each side of each reel cutting unit includes a front pivot link and a rear pivot link that are longitudinally spaced apart from one another and that are contained within a common longitudinal plane adjacent to one of the side plates of the reel cutting unit. The top end of each link is pivotally secured to the cutting unit carrier frame and the bottom end of each link is pivotally secured to the adjacent side plate of the reel cutting unit. If the reel cutting unit sees a rise or dip in the ground that is not encountered by the wheels of the gang reel mower itself, the reel cutting unit can, through the provision of the front and rear pivot links within the four-bark linkage, pivot or pitch fore and aft about a horizontal transverse pitch axis independently of the gang reel mower to allow the reel cutting unit to independently follow the ground contour that it is seeing at that moment in time. Thus, the front and rear pivot links of the four-bar linkages provide a first degree of freedom of motion for the reel cutting units, namely a pivoting or pitching back and forth about a substantially horizontal pitch axis.
The front and rear pivot links of the four-bar linkages in the Stiller patent are inclined towards one another as they extend downwardly. In other words, the top ends of the links are further apart than the bottom ends such that the distance between the links progressively lessens as the links extend downwardly such that the links converge towards one another. The two links never extend far enough downwardly to actually intersect or touch one another. However, the axes of the two links when extended further downwardly below the bottom ends of the links will intersect with one another at a focal point. This focal point represents the virtual pull point of the reel cutting unit, namely the point at which the propulsive force provided by the frame of the gang mower is effectively acting on the reel cutting unit to propel the reel cutting unit. The converging axes of the front and rear pivot links allow this virtual pull point to be located very low on the reel cutting unit and close to the ground, which is desirable in avoiding the application of any overturning moments on the reel cutting unit.
The four-bar pivot linkages as described above have been used by The Toro Company, the assignee of this invention, in a gang reel mower known as the Reelmaster 3100-D. In that product, the front and rear pivot links of the four-bar linkage create a virtual pull point that is slightly below and slightly to the rear of the axis of the rotatable reel of the cutting unit, as shown in FIG. 7 of the Stiller patent. This location of the virtual pull point is approximately aligned in a longitudinal sense with the center of gravity (c.g.) of the reel cutting unit so that there is little or no torque about the pull point tending to rotate the reel cutting unit in one direction or the other about the pull point when the cutting unit is up off the ground in a transport position. One can think of this as a neutral or balanced position in which the weight of the cutting unit is substantially, though not necessarily exactly, equally located on either side of the virtual pull point. Thus, when the cutting unit is down on the ground and is cutting grass, it has a generally neutral fore-and-aft weight distribution with approximately as much weight being seen by the front roller as the rear roller of the reel cutting unit. In this respect, it should be noted that this substantially neutral or balanced position can be one in which there is a very slight weight bias to the rear, i.e. the c.g. is just slightly behind the virtual pull point so that the reel cutting unit approaches the ground when it is being lowered towards the ground by the lift arm in a slight tail down orientation in which the rear roller is slightly lower than the front roller so that the rear roller hits the ground first.
The four-bar pivot linkages of the Stiller patent were an advance in the mowing art in allowing the creation of virtual pull points that were low on each reel cutting unit and that were substantially longitudinally aligned with the c.g. of the reel cutting unit. However, the Applicants have discovered that the provision of just one pull point is too limiting due to variations in grass conditions and an increasing desire in the art for improved after cut appearance from gang mowers. In certain grass conditions, the front and rear cutting units of a reel gang mower can leave marks in the cut grass swath where the rear cutting units overlap the front cutting units with the grass being rolled and cut twice in the overlap areas. Such streaks are objectionable where the appearance of the cut grass swath is important to the end user, e.g. on golf courses that host professional golf tournaments, other highly manicured golf courses, and the like. These users desire a cut grass swath that is as uniform in appearance from one side to the other as is possible, even though portions of the swath are actually acted on by the cutting units twice in the overlap areas whereas other portions of the swath are only acted on by the cutting units once in the non-overlap areas.
The Applicants have discovered that the aftercut appearance issues noted above can be solved by providing the user with the ability to adjust the pull points on the reel cutting units to be able to selectively change the fore and aft weight balance of the cutting unit. Accordingly, it would be a further improvement in the art if reel cutting units were provided which enable the user to easily pick and choose different pull point locations.